I agree that the Stone Sorcerer in
this Unearthed Arcana looks like a decent attempt. For example:
The Stone Sorcerer gets proficiency with shields, simple weapons, and martial weapons at 1st level. They also get the "Metal Magic" ability, which adds a lot of weapon-focused spells like Compelled Duel, Searing Smite, Elemental Weapon, and so forth to the Sorcerer spell list. And last but not least, they get the Stone's Durability ability. This gives them +1 hit point at 1st level, and +1 hit point per level-up. They can also use an Action to boost their AC when they're not wearing armor.
All that, at 1st level.
Then at 6th level, they get the Stone Aegis ability--an earth-based protection aura for one creature. The target takes less damage from bludgeoning, piercing, and slashing damage, and you can teleport to the warded creature as a reaction. It's an incredibly useful buff AND movement trick. (Useful, but I wouldn't say "powerful.")
The 14th and 18th level abilities look pretty excellent, but I haven't had a chance to test them out yet. One lets you deal extra force damage equal to your sorcerer level, and the top ability lets you expand your Stone Aegis to up to 3 creatures.
The only thing missing, IMO, is the Extra Attack ability that other martial characters get. But the Stone Aegis and Metal Magic abilities maybe make up for it.
TL;DR: folks who want a "martial Sorcerer" should check out Stone Sorcery, in Unearthed Arcana,
as a starting point. As far as UA content goes, it's one of the better attempts, and all it needs IMO is a bit of polish to fit your campaign. Add Extra Attack at 6th level, and give them an ASI at 10th level, maybe?